Lenticular device for an autostereoscopic display apparratus and method of producing the same

ABSTRACT

A method of producing a lenticular device for an autostereoscopic display apparatus includes providing a substrate having a surface which corresponds in shape to a desired surface profile for the array of lenticular elements, and providing an optical layer mixture of an optically birefringent material and a polymer precursor over the substrate surface. The optical layer is exposed to a stimulus for polymerizing the polymer precursor to have at least a polymer surface layer, thereby enclosing the material between the polymerized material and the surface to define lenticular elements. This method allows a simple polymerization process, forming a single layer, to complete the LC cell formation in the desired lenticular array shape.

The present invention relates to a lenticular device for anautostereoscopic display apparatus. The display apparatus comprises animage display device for providing a display output composed of rows andcolumns of pixels, and the lenticular device comprises an array oflenticular elements for directing the outputs from respective groups ofpixels in mutually different directions so as to enable a stereoscopicimage to be perceived.

Known autostereoscopic display apparatus of this type comprise a matrixLC (liquid crystal) display panel which has rows and columns of pixels(display elements) and which acts as a spatial light modulator tomodulate light directed therethrough from a light source. The displaypanel can be of the kind used in other display applications, for examplecomputer display screens for presenting display information in twodimensional form.

A lenticular sheet, for example in the form of a moulded or machinedsheet of polymer material, overlies the output side of the display panelwith its lenticular elements, comprising (semi) cylindrical lenselements, extending in the column direction, with each lenticularelement being associated with a respective group of two, or more,adjacent columns of display elements and extending parallel with thedisplay element columns.

In an arrangement in which each lenticule is associated with two columnsof display elements, the display panel is driven to display a compositeimage comprising two 2D sub-images vertically interleaved, withalternate columns of display elements displaying the two images, and thedisplay elements in each column providing a vertical slice of therespective 2D (sub) image. The lenticular sheet directs these twoslices, and corresponding slices from the display element columnsassociated with the other lenticules, to the left and right eyesrespectively of a viewer in front of the sheet so that, with thesub-images having appropriate binocular disparity, the viewer perceivesa single stereoscopic image.

In other, multi-view, arrangements, each lenticule is associated with agroup of more than two adjacent display elements in the row directionand corresponding columns of display elements in each group are arrangedappropriately to provide a vertical slice from a respective 2-D (sub-)image. As a viewer's head moves, a series of successive, different,stereoscopic views are perceived for creating, for example, alook-around impression. In view of the need for the lenticular elementsto be accurately aligned with the display pixels, it is customary forthe lenticular screen to be mounted over the display panel in apermanent manner so that the position of the lenticular elements isfixed in relation to the array of pixels.

WO 98/21620 discloses an improvement in the lenticular arrangement iscontrollable such that the lens action of the lenticular elements can beswitched on and off.

In an “on” setting, the lenticular elements behave as in theconventional arrangement. In the “off” setting, the lenticular elementsbehave as if they merely form a simple sheet of transparent material.Thus, with the lenticular elements in the off setting, and with thepixels of the underlying display panel being driven to present a 2-Dimage, this 2-D image is seen by both eyes of the viewer and byutilising all the available columns of pixels in the panel the viewerwill see a 2-D image whose horizontal resolution is considerablyincreased compared with that obtained for each stereo view.

The ability to switch the lenticular elements in this manner enables thedisplay apparatus to be used not only to provide stereoscopic images butto provide also higher resolution 2-D images, as required for textdisplay for example, when desired.

The ability to switch between the settings is achieved by forming thelenticular elements from an electro-optic material, whose refractiveindex can be altered by the selective application of electricalpotential. This material is filled between opposing electrodes whichdefine the desired lenticular shape. A liquid crystal material,generally a nematic liquid crystal, can be used with seals beingprovided around the periphery of the lenticular array to retain thematerial. Appropriate orientation layers are also provided.

With no potential applied across the material, the liquid crystalmaterial is oriented such that its refractive index, in the direction ofview, differs from, and more particularly is higher that of the materialused for the substrates/electrodes, and such that when a predeterminedpotential is applied to the electrodes, the liquid crystal is orientedsuch that its refractive index in the direction of view is changed andsubstantially matches that of the substrates/electrodes.

In this way a lens action of the lenticular elements can effectively beturned on and off.

FIG. 1 shows the known design concept. In FIG. 1, the stack from top tobottom consists of a glass plate 10 coated with ITO 12. On the ITO side,a negative lenticular structure 14 has been applied using a replicationtechnique. This structure has been coated with a (rubbed) polyimide 16,for LC molecule alignment. Inside the negative lenticular structure, LCmaterial 18 is present. The area containing the LC material 18 is closedusing a lower glass plate 20 with an ITO electrode layer 22, and coatedwith a rubbed polyimide layer 24. The two ITO layers 12,22 are used forthe control of the LC material.

The lenticular device comprises an array of juxtaposed parallellenticular elements in the form of convex cylindrical lenses. The lowerside is flat while the top side comprises a profiled (convex-ribbed)surface as determined by the contours of the lenticular elements.

FIG. 1 shows the optical effect in the “on” condition, on the left ofFIG. 1, and the optical effect in the “off” condition, on the right ofFIG. 1. In the “on” 3D mode, the lens focusing (shown schematically) canbe seen to have effect. The images of the different pixels associatedwith the lens are directed in mutually different directions towards aviewer's eyes by virtue of the lens action of the lenticular element sothat a viewer sees a different pixel column in each eye. The lens actionof the lenticular element forms an image of adjacent pixel columns closeto the eye positions. In the “off” 2D mode, the lens action is removedand the viewer sees the image of all pixels with each eye.

FIG. 2 shows the conventional manufacturing technique for the structureshown in FIG. 1. The manufacturing technique consists of traditionalmanufacturing steps that are as well used in, for example, STN-LCDmanufacturing.

As shown in FIG. 2, the two glass substrates are processedindependently, with cleaning, polyimide printing, baking and rubbingprocesses, with the seal formed on the substrate carrying the replicalenticular pattern. However, process steps might be slightly differentin detail and the seal can be applied on the opposite substrate as well.Conventional cell filling is used to form the LC material between thetwo substrates, as shown in the lower part of FIG. 2. As shown, thiscell formation comprises coupling, pamping, filling, lead bonding andproviding an antireflection coating.

There are a number of issues associated with these conventionalprocesses, and which present particular difficulties for forming thelenticular shaped LC layer.

There are difficulties in preventing too much LC material being providedin the lenticular layer, as a result of inaccurate pressing orinaccurate curvature of the lenticular elements. There may instead beinsufficient LC material in the lenticular layer, caused by too lowvacuum. Filling problems may result in the inclusion of bubbles orvacuum voids in the LC material. The processes also result in a verylong filling time for large size switchable lenticular devices (forexample of the order of hours). The manufacturing equipment is alsoexpensive, and requires high class clean room facilities.

In addition to problems resulting from the manufacturing requirements,the design itself has some disadvantages. The need for two ITO-coatedglass plates gives rise to a minimum distance of the switchablelenticular layer from the display panel, dependent on the thickness ofthe glass. For large size panels, the standard glass used has athickness of typically 700 μm, and for small size panels the glassthickness is typically 400 μm. As a result, the distance between theswitchable lenticular layer and the underlying display panel cannot bereduced beyond corresponding limits, which dictates the performance ofthe 3D panel.

The minimal lenticular distance also limits the design freedom for theoptics. In addition, the weight of the switchable lenticular arrangementrelative to the underlying display panel is significant, as is theadditional thickness.

According to the invention, there is provided a method of producing alenticular device for an autostereoscopic display apparatus, thelenticular device comprising an array of lenticular elements, the methodcomprising:

providing a substrate having a surface which corresponds in shape to adesired surface profile for the array of lenticular elements;

providing an optical layer mixture of an optically birefringent materialand a polymer precursor over the substrate surface; and

exposing the optical layer to a stimulus for polymerizing the polymerprecursor to form at least a polymer surface layer, thereby enclosing alenticular element array.

This method allows a simple polymerization process, forming a singlelayer, to complete the LC cell formation in the desired lenticular arrayshape. There can be no need for mask exposure steps as part of thepolymerization process nor any need for the use of chemicallyfunctionalized species. The polymer surface layer can thus besubstantially flat and of substantially uniform thickness.

The lenticular elements preferably comprise non-polymerized opticallybirefringent material, preferably electro-optic material, enclosedbetween the polymerized material and the substrate surface. Thenon-polymerized material is then electrically switchable to defineswitchable lens elements.

The optical layer mixture can be provided by a coating technique such asspin coating or slit coating, or by printing, doctor blade coating or byother techniques. The electro-optical material can comprise a liquidcrystal material.

The step of exposing the optical layer to a stimulus can compriseexposing the optical layer to UV radiation.

The method may further comprise manufacturing the substrate having asurface which corresponds in shape to a desired surface profile for thearray of lenticular elements, by:

providing a glass substrate;

providing a transparent conductive layer over the glass substrate; and

providing a replica layer having as its upper surface the surface whichcorresponds in shape to a desired surface profile for the array oflenticular elements.

The transparent conductive layer (e.g. ITO) acts as one of the controlelectrodes for the switchable lenticular device.

The manufacture of the substrate having the surface which corresponds inshape to a desired surface profile for the array of lenticular elementsmay further comprise:

providing a polyimide layer over the surface; and

baking and rubbing the polyimide layer.

A transparent conducting layer (e.g. ITO) can be applied over thediscrete polymer surface layer, to define a second control electrode forthe switchable lenticular device.

The invention also provides a lenticular device for an autostereoscopicdisplay apparatus, the lenticular device comprising:

an array of lenticular elements formed of a mixture of an opticallybirefringent material and a polymer precursor, the array of lenticularelements extending between a substrate, having an upper surface whichcorresponds in shape to the curved lenticular element surfaces, and apolymer top layer formed by polymerization of a portion of the polymerprecursor of the mixture.

Again, the polymer surface layer can be substantially flat and ofsubstantially uniform thickness.

The invention also provides an autostereoscopic display device,comprising:

a display device for providing a 2-dimensional output image, or aplurality of 2-dimensional output images for conversion to astereoscopic image; and

a switchable lenticular device of the invention.

Embodiments the invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 shows a known design of switchable lenticular lens arrangement;

FIG. 2 the known manufacturing method for producing the lens arrangementof FIG. 1;

FIG. 3 shows the manufacturing method for producing a lens arrangementof the invention, and shows the lens arrangement of the invention;

FIG. 4 shows a display device of the invention.

It should be understood that the Figures are merely schematic and arenot drawn to scale. In particular, certain dimensions may have beenexaggerated whilst other have been reduced. The same reference numeralsare used throughout the drawings to indicate the same or similar parts.

The invention provides a manufacturing process for a switchablelenticular device for use in an autostereoscopic display device, andwhich uses a liquid crystal material, which is formed without the needfor a vacuum filling process. Instead, a printing or spin coating (orsimilar) method can be used for the liquid crystal cell formation.

The applicant has developed the basic technology in the context ofgeneral liquid crystal display manufacture, and a brief discussion ofthis new technology will now be presented. EP1065553A1 describes thetechnology in further detail.

The proposed use of the technology to date is for the formation of astratified (i.e. segmented) light modulation layer.

A layer of a mixture of a polymer precursor and a liquid crystal (LC)material is deposited on a transparent substrate carrying an orientationlayer, after which the mixture is exposed to UV light in aphotolithographic step. In this step, the polymer precursor ispolymerized to form sidewalls between the desired pixels of the LCD.Subsequently, the rest of the mixture is exposed to UV light. Thistriggers a phase separation in which the polymer precursor ispolymerized to form a continuous top layer on top of the LC material. Asa result, the LC material is trapped between the polymer top layer, thepolymer sidewalls and the substrate, thus forming a plurality ofLC-filled polymer capsules on the substrate. The polymer top layerserves as a second substrate.

This process allows the layer of a mixture of a polymer precursor and aliquid crystal (LC) to be applied by a coating process, which simplifiesand reduces the cost of the fabrication process. It also enables thesecond substrate to be thinner than the conventional glass substrate.The polymerization process forms cavities for each liquid crystal pixel,so that pixel alignment is provided and the body of liquid crystal foreach pixel is trapped in position.

A drawback of this method is that several photolithography steps arerequired to form the separate LC pixels, and the development andproduction of masks is costly. These photolithography steps are requiredin particular to define the polymerized side walls of each pixel.Furthermore, this process requires a number of different UV exposuresteps, of different wavelengths and intensities, in order to define sidewalls which penetrate the full depth of the mixture, and a top shallowsurface layer of polymerized material.

The applicant has also proposed in WO 2005/015295 an alternative processin which a single exposure step is required. In this process, a stampingprocess is used to selectively deposit a chemically functionalizedspecies over the substrate. This gives parts of the substrate a highaffinity for the polymerizable material of the mixture (in particular ahigh affinity to partially polymerized material). During a single UVirradiation step, the high affinity regions result in the polymerizationconcentrating at those regions of the mixture. When the mixture ispartially polymerized, non-polymerized liquid tends to concentrate atthe spaces between the high affinity regions, thereby defining theliquid crystal cells, whereas the polymerized parts of the mixtureconcentrate at the top surface (where the irradiation intensity isgreatest) and at the high affinity regions, thereby defining side walls.

This process simplifies the UV irradiation process, but still requiresaccurate alignment of the stamp used to deposit the functionalizedspecies.

The concepts and technology underlying the techniques outlined abovehave been modified to provide a process for the manufacture of alenticular device for an autostereoscopic display device. The process ofthe invention will now be described with reference to FIG. 3.

The lenticular device comprises a single ITO glass substrate which isprovided with the replica lens template 32 which defines the lenssurface shape. The glass substrate (under the replica) is coated with anITO electrode layer 33. Again, after cleaning, polyimide printing,baking and rubbing is carried out to define the LC alignment layer. Thepolyimide may be provided by printing, spin coating, or other standardprocessing steps.

Standard processing steps are thus used from the LCD industry to definethe substrate 34 ready for the printing process.

The paintable/printable LC process 36 is then used to createdLC-material filled lenticular elements.

This process comprises the coating of the substrate using the mixture 38of LC material, a monomer and other components. The coating can becarried out using a doctor blade 40, although other coating technologiescan be used.

When the mixture is exposed with UV-light 42 the monomers are convertedinto polymer, which leads to the separation of the polymer phase fromthe LC material. This creates two layers, the lower one 44 containingthe LC material, and the upper one 46 containing the polymer which is(approximately) 15 μm thick

A lenticular structure containing LC material is thus created.

A counter electrode then is formed, for example by application of an ITOfoil 49, which is applied on top of the polymer film. This isappropriate for a stand alone version. However, when the switchablelenticular is used on top of a display, the ITO can be integrated into apolarizer structure. Other options and/or designs are as also possible.

The resulting structure can be used in the same way and in the sameapplications as the existing switchable lenticular device technology. Asshown, the structure is pass to an assembly plant for assembly with anunderlying display device.

This process prevents the use of excessive amounts of LC material in thelenticular layer because of the simplified filling process, whichcomprises an accurately controllable coating process. Problemsassociated with the use of a vacuum are avoided, including theprocessing time required, and the LC mixture can easily be made bubblefree.

The process enables a reduction in the number of expensive processingsteps, such as alignment, coupling, pamping and filling. Some of thesesteps are replaced by a coating step and an exposure step. This may alsoenable the processing equipment conditions to be relaxed (clean roomrequirements).

The lenticular device can be placed against the underlying display withthe polymer layer against the display device output surface. Thispolymer layer has a thickness in the region of 15 μm, and this enablesthe optical performance to be improved. The use of a single glasssubstrate enables overall weight and thickness reduction.

The LC layer thickness can be used as a design parameter. By varying theamount of LC material in the mixture, several designs for the stack canbe created. There are essentially three options:

(i) The polymer layer is not in contact with the replicated structure.In this case the LC material can freely flow through the paintedswitchable lenticular upon mechanical loading.

(ii) The polymer layer is just in contact with the replicated structure.In this case, the polymer layer closes each lenticular element of thereplicated structure.

(iii) The polymer layer closes each lenticular element of the replicatedstructure and extends partly into the lenticular element cavity. In thiscase, a mechanical fixture is present between the replicated structureand the polymer film across the entire lenticular array. As a result,the stack becomes mechanically more stable.

These three design possibilities can be selected by adjusting the amountand/or composition of the mixture of monomer and LC material as well asthe polymerization process conditions.

There are advantages to the use of a single glass plate, as explainedabove. The invention can however provide advantages even when two glassplates are to be maintained. In this case, after the application of themixture of monomer and LC material, a second ITO coated glass plate iscoupled with the mixture. The process flow for the painted switchablelenticular is then applied, of UV-based polymerisation and resultingphase separation, In this way, the second ITO containing glass plate ismechanically coupled by the polymer with the lower part of the stack. Asa result, a similar design is obtained as the conventional LC fluidcontaining switchable lenticular described with reference to FIG. 2.However, the vacuum filling technology is still avoided.

FIG. 4 shows the lenticular device of the invention formed on thesurface of a conventional 2-dimensional display device. For example thedisplay device 52 may be a conventional active matrix liquid crystaldisplay device, provided with a backlight 50. The lenticular device isshown as 54. The mounting of the device 54 to the front surface of thedisplay device may be achieved in different ways, as will be apparent tothose skilled in the art.

The display driving technique to provide stereo images will be as in forconventional switchable lenticular arrangements, and will also be knownto those skilled in the art.

The description above concerns only one detailed example of switchablelenticular device. Modifications to the design are of course possible.For example, the displays can be partly switchable. This requiressegmented electrodes, and this then enables part of the display to beoperating in 2D mode (with higher resolution) and part of the display tobe operating in 3D mode (with lower resolution).

In the example above, the application of voltage gives rise to the 2Dmode, and the 3D mode is the default mode with no voltage applied. It isof course possible to change the design so that the application ofvoltage to the lenticular device creates the 3D mode. This requires adifferent type of LC material, particularly negative refractive indexchange material, which is homeotropically oriented.

The example above shows a negative (concave) replicated structure.However, a positive (convex) structure can equally be used.

The painted LC material based switchable lenticular device can bedirectly applied on the colour filter plate of the underlying displaydevice, instead of a separate glass plate. As a result of the reducedthickness of the painted lenticular device, it is possible to stackseveral lenses (each with only one glass substrate), thus creating amulti-focal lenticular lens device.

In the above described embodiment, the lenticular device has an array ofelongate, cylindrical, lenticular elements. It will be understood thatthe lenticular sheet could instead comprise an array of spherical microlens elements instead, such spherical lens elements lenticular sheetsalready being known in the field of autostereoscopic display apparatus.

Also, the lenticular elements need not extent parallel to the pixelcolumns but could instead be slightly slanted with respect to the pixelcolumns, as described in EP-A-0 791847.

In the example given above, the phase-separation of the material thatprovides the top seal to the LC layer is induced by UV radiation. Itmay, however, also be possible to use solvent or temperature inducedphase-separable material.

As also mentioned above, the polymeric stratified-phase-separatedcomposite is known in the art, as well as the method of producing suchmaterials. Reference is made to U.S. Pat. No. 6,486,932, WO 02/42832, WO02/48281, WO 02/48282 and WO 02/48783.

By way of example, a suitable composition (which is also disclosed inthe article “Robust flexible LCDs with paintable technology” of JoostVogels et al, in The Journal of the SID Dec. 4, 2004) is as follows:

-   -   50 weight percent (wt %) of a liquid crystal mixture, for        instance the mixture E7, which is marketed by Merck;    -   44.5 weight percent (wt %) of photo-polymerizable        isobornylmethacrylate (supplied by Sartomer); and    -   4.5 weight percent (wt %) of a stilbene dimethacrylate dye:

The synthesis of this has been disclosed in PCT patent application WO02/42382 and which is hereby incorporated by reference, the twoacrylates being the polymer precursor; and

-   -   0.5 weight percent (wt %) of benzildimethylketal, which is        marketed by Ciba-Geigy under the trade name Irgacure 651.

The UV exposure of this material to provide the polymerization may forexample involve exposing the layer to UV light with a light intensity ofaround 0.1 mW/cm² for 30 minutes at 40° C.

The inclusion of a compound having a chromophore strongly absorbing inthe UV region of the electromagnetic spectrum, i.e., the stilbenedimethacrylate dye in the example above, causes the desired gradient inthe UV intensity through the layer. This effect may be amplified by theUV absorptions of the other components of the liquid, like the othercomponents of the polymer precursors and the electro-optical materials.Consequently, the polymerization reaction predominantly takes place atthe surface facing the UV source.

When other stimuli for triggering the polymerization reaction are used,care has to be taken that the polymerization reaction predominantlytakes place at the surface.

The example above provides optically switchable lens elements. Analternative way to provide a switchable lenticular arrangement forautostereoscopic displays is to have non-switchable lens elements, butwhich have different responses to different light polarizations. Apolarization switch arrangement can then control the state of thelenticular device. This polarization switch can be implemented as aswitchable LC device in series with the lenticular arrangement. Thisapproach is described in detail in WO 04/070451, and the methoddescribed above can be used to form the lenticular arrangement, forexample by providing full polymerization of the LC material mixture.

It should thus be apparent that the above-mentioned embodimentsillustrate rather than limit the invention, and that those skilled inthe art will be able to design many alternative embodiments withoutdeparting from the scope of the appended claims.

The invention claimed is:
 1. A lenticular device for an autostereoscopicdisplay apparatus, the lenticular device comprising: an array oflenticular elements formed on a substrate, the array of lenticularelements extending between a substrate surface, having an upper surfacewhich corresponds in shape to curved lenticular element surfaces, and apolymer surface layer; wherein the polymer surface layer is locatedimmediately above the array of lenticular elements; and wherein thepolymer surface layer has a depth that reaches beyond peaks of the uppersurface of the substrate and extends partly into each cavity thatdefines the lenticular shape of each respective lenticular element ofthe array, thereby enclosing the array of lenticular elements to form amechanical fixture comprising a plurality of polymer capsules filledwith a liquid crystal material.
 2. The device as claimed in claim 1,wherein the lenticular elements comprise a non-polymerized liquidcrystal material enclosed between the polymer surface layer and thesubstrate surface, and are electrically switchable.
 3. The device asclaimed in claim 1, wherein the polymer surface layer is substantiallyflat and of substantially uniform thickness.
 4. The device as claimed inclaim 1, wherein the upper surface of the substrate is provided with arubbed polyimide layer.
 5. The device as claimed in claim 1, wherein atransparent conducting layer is provided over the polymer surface layer.6. The device as claimed in claim 5, wherein the transparent conductinglayer comprises ITO.
 7. An autostereoscopic display device, comprising:a display device for providing one or more 2-dimensional output images,or a plurality of 2-dimensional output images for conversion to astereoscopic image; and a lenticular device including an array oflenticular elements formed on a substrate, the array of lenticularelements extending between a substrate surface, having an upper surfacewhich corresponds in shape to curved lenticular element surfaces, and apolymer surface layer; wherein the polymer surface layer is locatedimmediately above the array of lenticular elements; and wherein thepolymer surface layer has a depth that reaches beyond peaks of the uppersurface of the substrate and extends partly into each cavity thatdefines the lenticular shape of each respective lenticular element ofthe array, thereby enclosing the array of lenticular elements to form amechanical fixture comprising a plurality of polymer capsules filledwith a liquid crystal material.